Primacor and Dobutamine running @ same time?

It is a very common combination for our severe heart failure patients. Both drugs have a different pathway to stimulate the inotropy of the heart. Dobutamine works via your beta receptors stimulating the enzyme adenylate cyclase to promote formation of cAMP from ATP where cAMP will increase the intracellular calcium concentration that leads to inreased contractility. Milrinone is an PDE3-I (phosphodiesterase inhibitor class 3) that will inhibit the enzym phosphodiesterase so it no longer breaks down cAMP and as a result contractility increases. So both drugs can work synergistically.

In my experience milrinone will cause more afterload reduction as compared to dobutamine therefore hypotension is more of an issue. At the same time milrinone is less proaritmogenic than dobutamine. And milrinone will have a more profound effect in decreasing pulmonary hypertension as compared to dobutamine. So usually the last two effects are what prompts preference for adding milrinone as opposed to increasing the dosage of dobutamine.